Do visit Hogenakkal Waterfall that comes in between Bangalore & Coimbatore. But if you are planning in Summer then you can avoid this one as the heat becomes unbearable during summer. You can visit Isha Adi Yogi Centre in Coimbatore as well that is 30 KM away from Coimbatore railway station. 14D buses daily operate from Coimbatore to Isha Adi Yogi.
I was there in this Mahashivraatri. The place is so beautiful but the weather was too hot during that time as well.
Try camping at kolukkumalai you can see sun rise at the peaks and an awesome trekking experience.
I do have some contacts try them. Contact: Mr.Thamil selvan 9159852238 (Rs.1500 per person includes accommodation and food (snack at evening, dinner, breakfast and lunch)
You have to reach there by Jeep to the camp Rs.3700 (max 7-8 person) a jeep Contact: Black eagles camp 9605830850
Koukkumalai is one of the best paces to stay in munnar. The Mountains and the sunset there is unbeatable. Don't miss Marayur where you can find the sandalwood forest, sugarcane fields, how jaggery is produced from sugarcane...etc etc. But the temperature now at Munnar is not that much cold but is moderate. Anyway have a nice trip 👍